Originally Posted by rickg523

You're crossing an international border. There are some accommodations because of the trade and business cross-border connections. But YOU should consider it as traveling abroad. Bring your passport. Yes you can use the passport card, but if you have the passport why bother? The card seems to be one of those accommodations for regular commercial travelers.
Also, check with your mobile provider. Outside of T-Mobile, they definitely treat Canada as abroad and charge accordingly.